1. Field of the Invention
The invention relates to a cassette case for holding a plurality of substrates therein such as liquid crystal panels.
2. Description of the Related Art
A cassette case can hold a plurality of substrates at a time, and hence has been widely used for carrying a plurality of substrates at a time between fabrication steps, or subjecting a plurality of substrates to thermal treatment at a time. Namely, such a cassette case can provide higher productivity as it can hold the greater number of substrates.
However, there would arise a problem that a cassette case becomes heavier as it holds the greater number of substrates therein. Hence, there have been suggested a variety of cassette cases which could hold a lot of substrates, but could prevent an increase in weight thereof.
One of such cassette cases is illustrated in FIG. 1. The illustrated cassette case includes a frame F comprising a rectangular upper frame portion 10a made of metal such as aluminum, a lower frame portion 10b having the same shape as that of the upper frame portion 10b, and a plurality of pillar members 12 for connecting the upper and lower frame portions 10a and 10b to each other therethrough with the upper and lower frame portions 10a and 10b being spaced away from each other by a height.
A pair of upper slide shafts 14a are carried in parallel between facing sides of the upper frame portions 10a. Similarly, a pair of lower slide shafts 14b are carried between facing sides of the lower frame portions 10b in parallel with each other and also in parallel with the upper slide shafts 14a. The upper slide shafts 14a are spaced away from each other by the same spacing as a spacing between the lower slide shafts 14b.
A pair of bar-shaped upper support members 16a having almost the same length as a spacing between the upper slide shafts 14a are carried just below the upper slide shafts 14a. There are disposed blocks 16c on the upper slide shafts 14a, and the upper support members 16a are fixed to the upper slide shafts 14a by being threaded to the block 16c by means of screws 16e with the upper slide shafts 14a being sandwiched between the blocks 16c and the upper support members 16a. Similarly, a pair of bar-shaped lower support members 16b having almost the same length as a spacing between the lower slide shafts 14b are carried on the lower slide shafts 14b. There are disposed blocks 16d just below the lower slide shafts 14b, and the lower support members 16b are fixed to the lower slide shafts 14b by being threaded to the block 16d by means of screws 16e with the lower slide shafts 14b being sandwiched between the blocks 16d and the lower support members 16b.
There are three substrate support members 18a, 18b, 18c carried in a row between each of the upper and lower support members 16a and 16b. The substrate support members 18a, 18b, 18c carried between one of the upper and lower support members 16a and 16b are disposed in facing relation with the substrate support members 18a, 18b, 18c carried between the other of the upper and lower support members 16a and 16b. The substrate support members 18a, 18b, 18c have the same shape, and are formed at surfaces thereof facing with each other with a plurality of grooves 18d extending horizontally, namely, in a direction perpendicular to a length-wise direction of the substrate support members 18a, 18b, 18c. The grooves 18d are arranged vertically, or in a length-wise direction of the substrate support members 18a, 18b, 18c.
The upper and lower support members 16a and 16b are carried at the upper and lower slide shafts 14a and 14b so that the members 16a and 16b are in advance spaced away from each other by a distance equal to a width of a substrate 20. Thus, a substrate 20 is inserted into the groove 18d formed on surfaces of the substrate support members 18a, 18b, 18c. The cassette case holds the same number of the substrates 20 as the number of the grooves 18d (only one substrate 20 is illustrated in FIG. 1 for simplification of the drawing).
The upper and lower support members 16a and 16b together with the substrate support members 18a, 18b, 18c can be slid along the upper and lower slide shafts 14a and 14b, after the screws 16e fixing the blocks 16c to the upper and lower support members 16a and 16b are released. Hence, when substrates having different width are to be inserted into the grooves 16d, a spacing between the facing substrate support members 18a, 18b, 18c may be varied in accordance with the width of the substrates 20 by sliding the upper and lower support members 16a and 16b together with the substrate support members 18a, 18b, 18c.
The upper and lower frame portions 10a and 10b and the pillar members 12 tend to receive impact and/or oscillation when a cassette case is being transferred, and hence are made of material having great strength such as metal and assembled with screws and nuts. The substrate support members 18a, 18b, 18c are made of resin in order to prevent the substrates 20 made of glass from being abrased, lighten the cassette case, and ensure heat-resistance for the cassette case.
As illustrated in FIG. 2, the substrate support members 18a, 18b, 18c are formed at longitudinal ends thereof or upper and lower ends thereof with tags 18e having a smaller transverse cross-sectional area than that of the substrate support members 18a, 18b, 18c. The substrate support members 18a, 18b, 18c are fixedly connected to the upper and lower support members 16a and 16b by the tags 18e being threaded to the upper and lower support members 16a and 16b by means of screws 21.
When the substrates 20 being held in the cassette case are thermally treated, the frame F as well as the substrates 20 is exposed to high temperature, and thus both of the frame F and the substrates 20 thermally expand. With the pillar members vertically, thermally expanding, the frame F vertically, thermally expands. However, since the pillar members 12 made of metal have a different thermal expansion coefficient from that of the substrate support members 18a, 18b, 18c,the pillar members 12 and the substrate support members 18a, 18b, 18c thermally expand in different degrees. As a result, the substrate support members 18a, 18b, 18c become curved in accordance with a difference in a thermal expansion coefficient between the pillar members 12 and the substrate support members 18a, 18b, 18c.
Hence, the positional relationship between the grooves 18d disposed in facing relation varies accordingly, resulting in that the substrates cannot be inserted into the grooves any more, and that the substrates 20 having been inserted into the grooves 18d cannot be taken out thereof. In particular, when a machine is employed for automatically inserting substrates into grooves and taking substrates out of grooves, the substrates may be abrased or damaged at worst, because such a machine merely inserts substrates into and take substrates out of the grooves without consideration as to whether the substrates can be smoothly inserted into or taken out of the grooves.
The upper and lower frame portions 10a and 10b of the frame F is constructed by connecting metal bars at their edges with each other and fixing them to each other by means of screws. Thus, each time the frame F is subject to thermal treatment, a fastening force of the screws is made to weaken, resulting in that an outer shape of the frame F is deformed, and that it would be difficult for the frame F to keep sufficient rigidity thereof. In addition, there is a limitation with regard to the number of the pillar members 12 ensuring transverse rigidity, from the standpoint of reduction in weight of a cassette case. For those reasons, it is quite difficult for the frame F to have sufficient rigidity. This is accompanied with a problem that when a machine is employed for transferring the cassette case, it would be impossible to precisely position the cassette case.
FIG. 3 illustrates another example of conventional cassette cases for holding a plurality of substrates therein, suggested in Japanese Unexamined Patent Publication No. 7-101481 published on Apr. 18, 1995. The illustrated cassette case includes a pair of outer frames 50a and 50b spaced away from each other. Between the outer frames 50a and 50b are supported a pair of slide shafts 52. A pair of panel holding plates 54a and 54b disposed in facing relating with each other are formed at an outer surface thereof with a plurality of grooves 54c. A plurality of panels 56 are supported between the panel holding plates 54a and 54b by being inserted into the facing grooves 54c. The panel holding plate 54a is fixed to the outer frame 50a, whereas the panel holding plate 54b is fixed to a lock-unlock unit 60 through supports 58. In normal condition, the lock-unlock unit 60 is locked, but if the unit 60 is unlocked, the lock-unlock unit 60 together with the panel holding plate 54b can be slid along the slide shafts 52. Thus, panels having different width can be supported between the panel holding plates 54a and 54b.
The cassette case illustrated in FIG. 3 has the same problems as the above mentioned ones.